In a switch-mode DC to DC (DC-DC) converter, a switching frequency of a switch is higher than 10 KHz, so a current of the filter inductor has two components. One is the DC current and the other is high frequency AC ripple current. In a switch-mode AC to DC (AC-DC) converter (i.e. an active power factor correction (PFC) circuit), a current of the filter inductor also contains two components. One is the high frequency AC ripple current. The other one is the AC current with a low frequency below 400 Hz, and it is considered as the DC current compared to the switching frequency. Therefore, an operational inductor that contains both DC current component and high frequency AC ripple current is called a DC filter inductor.
The DC current component of the DC filter inductor forms a massive magnetic potential in the magnetic circuit. In order to avoid the saturation of the magnetic core as the magnetic core plays a vital role in raising the level of magnetic flux. It is required to increase/add the gap resistance (i.e. air gap) to the magnetic core, which reduces DC flux of the flux path, especially to those magnetic cores that are made of materials such as a ferrite, a silicon steel and an amorphous ferromagnet. As shown in FIG. 1 of an exemplary conventional embodiment indicating a single-phase inductor, a winding L is wrapped around middle arms of an EE type core which have air gaps. Furthermore, for a three-phase inductor, three windings are wrapped around three core arms respectively and each core arm has an air gap.
As current flows through the winding L, magnetic fields will be generated not only in the core and the air gap but also inside the winding L. The magnetic field of the winding L is composed of an air-gap magnetic field strength Ha and a bypassing magnetic field strength Hb. So a high frequency AC current flowing through the winding causes an AC winding loss which contains an air-gap magnetic field strength loss and a bypassing magnetic field strength loss. Using Litz wire as the winding L is one of the known skills for reducing the air-gap magnetic field strength loss, and is designed to reduce the skin effect loss and proximity effect loss. However, the bypassing magnetic field strength loss can not be reduced by the replacement the Litz wire and the bypassing magnetic field strength Hb is irrelevant to either shape or structure of the winding L. As shown in FIG. 1, the bypassing magnetic field strength Hb is in a linear relation of a distance x between the winding L and the air gap. In other words, Litz wire type winding remains AC winding loss.
In general, winding loss may cause the winding temperature rising. As shown in FIG. 2, a heat dissipating metal 200 is needed and is disposed inside the winding, as the winding loss generates undesirable heat. However, due to the existence of the bypassing magnetic field strength Hb, an eddy current is induced on the heat dissipating metal 200 resulting in additional winding loss.
Further, FIG. 3 shows an exemplary conventional embodiment indicating an UU type inductor that has two windings W1, W2 and two air gaps g1, g2. The AC magnetic potential is formed on the magnetic circuit as AC current flows through the winding W1, W2, and is mostly imposed on sides of the air gaps g1, g2. As shown in FIG. 3, when the air gaps g1, g2 are not covered by the winding W1, W2, the imposed magnetic flux of the air gaps g1, g2 will form magnetic field strengths on the edge of the inductor, which brings the near-field magnetic interference.
Therefore, there is one of the needs for a new inductor device which minimizes winding losses.
Some Exemplary Embodiments
These and other needs are addressed by various embodiments of the disclosure, wherein an approach is provided for minimizing winding losses and near-field magnetic interference (e.g., Alternating Current (AC) winding loss) of a Direct Current (DC) filter inductor device and an associated manufacturing method by reducing the bypassing magnetic field strength Hb inside the winding.
According to one aspect of an embodiment of the disclosure, a device for a direct current filter inductor comprises a magnetic core having at least one air gap, and at least one first winding and at least one second winding, which are connected to each other in parallel that having a mutual inductance, and are wrapped around the magnetic core respectively, wherein a difference between a first inductance of the first winding and the mutual inductance is smaller than a difference between a second inductance of the second winding and the mutual inductance; a Direct Current (DC) resistance of the first winding is larger than a DC resistance of the second winding; and the first winding is closer to the air gap compared to the second winding.
In an embodiment, the first winding has a wire diameter that is smaller than a wire diameter of the second winding.
In an embodiment, the first winding and the second winding are wrapped around the magnetic core separately. The first winding is fully or partially wrapped around the air gap.
In an embodiment, the device further comprises an inductance element connected to the first winding and the second winding in parallel or in series.
In an embodiment, the difference between the first inductance and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, the first inductance is equal to the mutual inductance.
In an embodiment, the device further comprises an inductance element connected to the first winding in series when the first inductance is smaller than the mutual inductance, wherein the first winding and the inductance element are connected to the second winding in parallel, and a difference between the summation of the first inductance and an inductance of the inductance element and the mutual inductance is smaller than the difference between the second inductance and the mutual inductance. The difference between the summation of the first inductance of the inductance element and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, wherein a DC resistance summation of the first winding and the inductance element is larger than the DC resistance of the second winding.
In an embodiment, the magnetic core is an EE type core that comprises a middle arm and two side arms, wherein the middle arm has the air gap, the first winding is wrapped around the middle arm, and the second winding is wrapped around the first winding.
In an embodiment, the magnetic core is an UU type core formed by two oppositely U-shaped core, and each U-shaped core comprises a longitudinal arm and two latitudinal side arms that are extended orthogonally from two ends of the longitudinal arm respectively. The latitudinal side arms of the U-shaped core are abutted adjacent to the corresponding latitudinal side arms of the other U-shaped core, thereby forming the two air gaps in between, and two first windings are wrapped around the corresponding air gaps and two second windings are wrapped around the corresponding longitudinal arms.
In an embodiment, the magnetic core is an EI type core formed by coupling a substantially E-shaped core to a magnetic bar, and the E-shaped core comprises three longitudinal arms and a latitudinal arm, each longitudinal arms has a first end that is extended orthogonally from the latitudinal arm, and second ends of the longitudinal arms are disposed adjacent to the magnetic bar with a corresponding air gap. Three first windings are wrapped around the corresponding longitudinal arms, and three second windings are wrapped around the corresponding longitudinal arms
In an embodiment, the device further comprises a first current sensing element connected to the first winding in series, and is configured to sense current flowing through the first winding.
In an embodiment, the device further comprises a second current sensing element connected to the second winding in series, and is configured to sense current flowing through the second winding.
In an embodiment, the first winding has a first wire or a multi-stand wire, and the second winding has a second wire, a copper foil winding or a PCB winding, wherein a wire diameter of the first wire is smaller than a wire diameter of the second wire.
According to another aspect of an embodiment of the disclosure, a device for a direct current filter inductor comprises a magnetic core, at least one first winding and at least one second winding. The first winding has a first end and a second end. The second winding has a first end and a second end. The first end and the second end of the first winding are connected to the first end and the second end of the second winding, respectively. The first winding and the second winding has a mutual inductance, and a difference between a first inductance of the first winding and the mutual inductance is smaller than a difference between a second inductance of the second winding and the mutual inductance. A DC resistance of the first winding is larger than a DC resistance of the second winding.
In an embodiment, the first and the second windings are separately wrapped around the magnetic core or wrapped around the magnetic core together.
In an embodiment, the device further comprises an inductance element connected to the first winding and the second winding in parallel or in series.
In an embodiment, the difference between the first inductance and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, the first inductance is equal to the mutual inductance.
In an embodiment, the device further comprises an inductance element connected to the first winding in series when the first inductance is smaller than the mutual inductance, wherein the first winding and the inductance element are connected to the second winding in parallel, and a difference between the summation of the first inductance and an inductance of the inductance element and the mutual inductance is smaller than the difference between the second inductance and the mutual inductance. The difference between the summation of the first inductance and the inductance of the inductance element and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, a DC resistance summation of the first winding and the inductance element is larger than the DC resistance of the second winding.
In an embodiment, the device further comprises a first current sensing element connected to the first winding in series, and is configured to sense current flowing through the first winding.
In an embodiment, the device further comprises a second current sensing element connected to the second winding in series, and is configured to sense current flowing through the second winding.
In an embodiment, the first winding has a first wire or a multi-stand wire, and the second winding has a second wire, a copper foil winding or a PCB winding, wherein a wire diameter of the first wire is smaller than a wire diameter of the second wire.
According to yet other aspect of another embodiment of the disclosure, a manufacturing method for a direct current filter inductor comprises step of providing a magnetic core; wrapping at least one first winding and at least one second winding around the magnetic, wherein a mutual inductance formed by the first and the second winding; configuring a difference between a first inductance of the first winding and the mutual inductance being smaller than a difference between a second inductance of the second winding and the mutual inductance, and a DC resistance of the first winding is larger than a DC resistance of the second winding; and coupling the first winding and the second first winding in parallel.
In an embodiment, the magnetic core has at least one air gap, and the first winding is closer to the air gap compared to the second winding.
In an embodiment, the method further comprises act of wrapping the first winding is fully or partially around the air gap.
In an embodiment, a first end and a second end of the first winding are connected to a first end and a second end of the second winding, respectively.
In an embodiment, the mentioned step of wrapping the first winding and the second winding around the magnetic core further comprises step of wrapping the first and the second windings separately or together around the magnetic core.
In an embodiment, the method further comprises acts of providing an inductance element connected to the first winding and the second winding in series or in parallel.
In an embodiment, the steps of configuring the difference between the first inductance of the first winding and the mutual inductance being smaller than the difference between the second inductance of the second winding and the mutual inductance further comprises step of configuring the difference between the first inductance and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, the method further comprises step of configuring the first inductance being equal to the mutual inductance.
In an embodiment, the method further comprises step of providing an inductance element connected to the first winding when the first inductance is smaller than the mutual inductance, wherein the first winding and the inductance element are connected to the second winding in parallel, and a difference between the summation of the first inductance and an inductance of the inductance element and the mutual inductance is smaller than the difference between the second inductance and the mutual inductance.
In an embodiment, the difference between the summation of the first inductance and the inductance of the inductance element and the mutual inductance is smaller than ⅓ of the difference between the second inductance and the mutual inductance.
In an embodiment, the method further comprises step of configuring a DC resistance summation of the first winding and the inductance element being larger than a DC resistance of the second winding.
In an embodiment, the method further comprises step of providing a first current sensing element connected to the first winding in series.
In an embodiment, the method further comprises step of providing a second current sensing element connected to the second winding in series.
Accordingly, the embodiments of the present disclosure separating the AC and DC current components, thereby two independent inductance windings connected in parallel are wrapped around a same arm of the magnetic core, which achieves not only reducing AC winding loss and easier for current sensing, also improves the flux distributions around the air gap for reducing the magnetic interference.
Still other aspects, features and advantages of the disclosure are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the disclosure. The disclosure is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the disclosure. Accordingly, the drawings and description are to be regarded as illustrative, and not as restrictive.